Between Sea and Land: In Praise of Interstices

Wetlands — mangroves, swamps and mud plains — are transient, in-between spaces that often go uncategorised and overlooked, but protecting the fringes of the familiar is essential for maintaining biodiversity across the whole planet.

Image by Max Ridgeway via Unsplash

As humans, we are trained to look to the middle, not the outer edges. The peak of the mountain, the heart of the rainforest, the crowning corals of the reef. But what of those other, outer spaces, those places lost in the in-between? The shores that are not quite beaches, where the tidelines smack against bare rock. The impenetrable tangles of mangroves that separate rainforest and river, the seagrass beds beside the reef. These places are hard to define and hard to experience. But that doesn’t mean they lack significance, in fact, wetlands are where landscapes and ecosystems collide and overlap and interact, they are complex sites of evolutionary ingenuity.

Wetlands – swamps, marshes, lakes, mudflats, mangroves and coral reefs – can be natural or artificial, static, flowing, fresh or saline. Wetlands lack the stability of a landscape, they lack the depth of the ocean. They are transient, they ebb and flow with the tides and seasons, at once fragile and resilient. Wetlands are an ecosystem that are defined not by what they contain, but by what they themselves define – oceans, rivers, rainforests. Wetlands are inaccessible, physically as well as conceptually. We cannot bushwalk through them, or swim over them. They are hard for us to use (the colonial metric of significance) and thus they have long been overlooked and undervalued as nothing more than the in-between. The Indigenous people of this land refer to such places as ‘sea country’, and in Yolngu language, this concept, ganma, has a double meaning — referring to the meeting and mixing of [sea] water … and fresh water from the land” as well as meaning “two-way learning.”

Australia’s northern and eastern shores are home to approximately 11,500 km2 of mangrove forests, the third largest area of mangroves in the world after Indonesia and Brazil. Mangrove forests are often dominated by only one or two plant species, but they are incalculable in the support they provide for biodiversity in other regions; they are womb, nursery, feeding ground, breeding site. Mangrove presence is directly linked to offshore abundance of adult fish, with 80% of global catches directly or indirectly dependent on mangrove systems at some stage in their lifecycle.1 Keystone species on coral reefs including sharks, parrotfish and groupers reproduce and spend their juvenile years protected by the dense web of roots before making the journey out to the reef. Birds, reptiles and amphibians from the land nest and hunt in the canopies.

Mangroves protect coastal areas from erosion, flooding, storm surges and tsunamis by dissipating wave energy with their massive and complex root systems, which also allows fine sediment to be dispersed and retained by the environment, absorbing pollutants and improving water quality offshore. Mangroves play a crucial role in the carbon cycle, holding an estimated three billion metric tonnes of carbon in their wood and soil — more than the world’s tropical forests.

As coastal population density increases, substantial areas of mangrove forest are replaced to provide urban and industrial lands, rice and salt production, and tourism related infrastructure. Thirty-five percent of global mangrove forests have been lost since 1980, and they continue to decline at a rate of one to two percent annually, an estimate that will grow exponentially with the effects of rising seas and warming climates.3 4

Mangroves, like all wetlands, contribute to global systems of biodiversity and carbon sequestration, but their unique vulnerability to localised exploitation poses a challenge for management. The global importance of wetlands wasn’t recognised until the 1971 signing of international conservation treaty, the Ramsar Convention. Australia currently has sixty five Ramsar wetlands covering an area of over 8.3 million hectares, and a further nine hundred nationally important wetlands are listed on the Australian Wetlands Database, but there are countless more that go unlisted and uncategorised.

Interfaces between ecosystems deserve our attention not only because they are vulnerable to threats from all sides, but because they emerge from the compounded resilience and diversity of their overlapping terrains. Wetlands are sites where species can collide and interact, producing unique adaptations and exquisite examples of evolutionary ingenuity. Estuarine swamps, mangroves and mudplains are more than just the in-between, an ecological bardo, they are the convergence of their overlapping neighbours, resulting in more than the sum of their parts. These are places that have no need for arbitrary boundaries, they are sites of growth, collaboration and communication between landscapes. When humans muck out mangroves for concrete shorelines, swap saltmarshes for boardwalks and let skyscrapers grow from swamps, we create new, neat boundaries, but rather than creating a new habitat, a new space, a new opportunity for interaction and evolution, we simply create a divide.

As we enter this age of the Anthropocene, we need to recognise that change isn’t happening in the middle of the state or the metropole. Change is happening on the fringes – on the rising tidelines, in the brackish waters where inshore run-off ebbs and flows to salt, and on the mudplains slowly receding under urban sprawl. Change is happening in international waters, in the weather systems that transcend continents, in the decades of far north Queensland droughts that years later suck the southern banks of the Darling River dry. These places deserve our attention, and our respect.

Homing in on the interconnectivity of the Earth’s systems is critical for planning and managing the future of the planet, but so is redefining our criteria for ‘place’. By defining and categorising places based on human experience, human timescales and human use, we risk overlooking landscapes not localised to our existence, like wetlands, which transcend their apparent cartography as major global systems. These are spaces that are shared with future generations too. Managing and conserving biodiversity, and even just maintaining basic ecosystem function, in the coming decades will mean a radical redefining of ecological boundaries in space and in time. Like mangrove roots in silt, we are all entangled in our global future — we, not just as humans, but as landscapes, seascapes and the places in between.


1. Pia Laegdsgaard and Craig Johnson2001. Why do juvenile fish utilise mangrove habitats? Journal of Experimental Marine Biology and Ecology. 257: 2, 229-253.
2. FAO 2007. The World’s Mangroves 1980–2005. FAO Forestry Paper. Rome: Food and Agriculture Organisation of the United Nations
3. Valiela, I., Bowen, J. L. & York, J. K. 2001. Mangrove forests: one of the world’s threatened major tropical environments. BioScience, 51, 807–815.
4. Dierberg, F. E. & Kiattisimkul, W. 1996. Issues, impacts, and implications of shrimp aquaculture in Thailand. Environmental Management, 20, 649-666

World Wetlands Day is celebrated annually on February 2 to mark the signing of the Ramsar Convention in 1971.

Liberty Lawson is the Content Editor and Knowledge Translation Officer at the Sydney Environment Institute. She is currently completing an interdisciplinary PhD at the University of Sydney, exploring tactics for marine conservation through science communication, environmental art and artificial coral reefs.